Magnetic head with gaps spaced as a function of the distance between recorded lines of information

ABSTRACT

An apparatus for the magnetic recording of gradient information wherein a magnetic gradient of given length is reproduced on a magnetic medium. A readout magnetic head is provided for sensing the recorded gradient information and a writing head is used to reproduce the gradient information onto an extended portion of a magnetic member containing the gradient information. Either the readout head or the writing head is provided with means for adjusting the distance between the two heads. The readout head and the writing head may be positioned opposed from one another so as to sense gradient information on a master copy of magnetic material and reproduce the gradient information on a magnetic member used for positioning machine tools or the like.

United States Patent Uemura [4 Mar. 28, 1972 54 MAGNETIC HEAD WITH GAPSSPACED 2,558,249 6/1951 Hewlett et al ..340/174.1 AS A FUNCTIONOF THE DITANCE 2,804,499 8/1957 Botts ...179/100.2 BETWEEN RECORDED LINES OF3,267,448 8/1966 Gonther.. ...340/l74.l 3,277,453 10/1966 Michel...179/100.2

INFORMATION 3,402,350 9/1968 Shellabarger 1 79/1002 2,332,573 10/1943Hibschman et al.

Continuation of Ser. No. 732,248, May 27, 1968, abandoned.

Foreign Application Priority Data May 31, 1967 Japan ..42/35111 11.5. C1..340/174.1 P, 340/174.1 L 1m. 01 ..Gllb 5/86, G1 lb 5 02 Field ofSearch ..346/74 M; 340 174.1 P, 174.1 A;

179/1002 RE, 100.2 CA, 100.2 E; 324/70 B, 172

References Cited UNITED STATES PATENTS Primary Examiner-Remard KonickAssistant ExaminerVincent P. Canney Attorney-Hill, Sherman, Meroni,Gross & Simpson ABSTRACT An apparatus for the magnetic recording ofgradient information wherein a magnetic gradient of given length isreproduced on a magnetic medium. A readout magnetic head is provided forsensing the recorded gradient information and a writing head is used toreproduce the gradientinformation onto an extended portion of a magneticmember containing the gradient information. Either the readout head orthe writing head is provided with means for adjusting the distancebetween the two heads. The readout head and the writing head may bepositioned opposed from one another so as to sense gradient informationon a master copy of magnetic material and reproduce the gradientinformation on a magnetic member used for positioning machine tools orthe like.

5 Claims, 8 Drawing Figures CROSS REFERENCE TO RELATED APPLICATION Thisapplication is a continuation of my copending Ser. No. I

732,248 filed May 27, 1968 and now abandoned.

BACKGROUND OF THE INVENTION l. Field of the Invention This inventionrelates to a magnetic recording method and device for precisegraduation.

2. Description of the Prior Art Machine tools, for example, must beequipped with a precise scale for processing use, and the precision ofthe machine tools is determined by the precision of the scale. and,therefore, the precision of the scale is of prime importance in the art.One scale that has heretofore been used is a magnetic scale which hasreference divisions, commonly referred to as magnetic grating, formed byrecording, for example, rectangular or sinusoidal signals of a certainwavelength on a glass or metal strip which has magnetic powder depositedthereon.

However, large or bulky machine tools require the use of long andprecise scales. Such long and precise scales encounter difficulties infabrication, in carrying, shipping and in mounting operations and so on.To avoid these difficulties, it is the practice in the art that aplurality of short precise scales jointed together are mounted onlarge-sized machine tools, but this conventional method presents aproblem as it is extremely difficult to join the scales within an errorof several microns. Accordingly, it is highly desirable that precisegraduation be possible after mounting of the scale members on themachine tools.

SUMMARY OF THE INVENTION It is one-object of this invention to provide arecording method and device which can be used with large-sized or bulkymachine tools.

It is another object of this invention to provide a recording method anddevice which can be used for measuring the mechanical precision ofmagnetic recording and reproducing devices.

Other objects, features and advantages of this invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings, wherein like reference numerals throughout thevarious views of the drawings are intended to designate similar elementsor components.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagramillustrating one example of this invention;

FIG. 2 is a schematic diagram showing one example of a scale memberemployed in this invention;

FIG. 3a is a cross-sectional view taken along the line IIIa "la in FIG.1;

FIG. 3b is a fragmentary side view'of-FIG. 1;

FIG. 4 is a plan view showing one example of a fine-control unit of theright head illustrated in FIG. 1;

FIGS. 5 and 6 are diagram waveforms for explaining this invention; and

FIG. 7 is a schematic diagram showing another example of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the drawingsa detailed description will be given of one example of this invention.

In FIG. 1 there is illustrated one embodiment of a recording deviceproduced according to this invention. Reference numeral 1 indicates ascale member consisting of a magnetic medium having reference divisionlines marked on one end portion A by precise magnetic grating asillustrated in FIG. 2.

A writing head 4 is provided with a signal coil 5. Reference numeral 6designates a mount on which a readout head 2 and the writing head 4 aremounted at a predetermined distance B from each other. The mount 6 isadapted to slide on a track 6' extended along the scale member 1.Reference character D identifies a detector circuit connected to thereadout head 2, P a waveform shaping circuit for shaping the output ofthe detector circuit D into a rectangular signal and R an amplifiercircuit for amplifying the output of the waveform shaping circuit P andapplying the amplified output to the writing head 4. It is preferredthat the readout head 2 and the writing head 4 are multi-gap heads suchas disclosed in my US. Pat. No. 3,308,449.

As shown in that patent, the gaps of the head are spaced by a multipleof A ,2, where A a is the spacing between the individual lines of therecorded information.

FIGS. 3a and 3b illustrate one example of a structure for sliding themount 6 on the track 6, in which reference numeral 7 indicates a spacerfor securing the readout head 2 to the mount 6 and 7 another spacer forslidably disposing the writing head 4 on the mount 6. That is, the mount6 is engaged with the dovetailed portion of the track 6 in a manner toslide along the scale member 1, and the writing head 4 can be finelyadjusted in the lengthwise direction of the track 6 so as to be spacedapart from the readout head 2 exactly at a predetermined distance B.

FIG. 4 shows one example of a structure for fine adjustment of thewriting head 4 in which reference numeral 8 designates a rod formed of anonmagnetic material and fixed to the lower end of the writing head 4, 9and 9' projections provided on the mount 6 and 10 and 10 pins which areinserted into apertures 11 and'll bored through the one projection 9 andfixed to the other projection 9 through holes 12 and 12 which are formedin the rod 8 in a manner to slidably support the rod 8. Referencenumeral 13 identifies a plate spring interposed between the projection 9and the rod 8, which always pushes the rod 8 to the right as seen on thedrawing. Reference numeral 14 indicates a screw for fine control. Thescrew 14 is screwed in from the side of the projection 9' and pushes theside of the rod 8 against the plate spring 13 to control the position ofthe writing head 4. In FIG. 3b the spacer 7' is fixed and its contactface with the writing head 4 is formed to be slidable.

With such an arrangement, the reference divisions, formed by magneticgrating previously recorded on the portion A of the scale member 1 areread out by the readout head 2 and is then written on another portion ofthe scale member I by the writing head 4. Accordingly, accurategraduation can be effected on the right side of the portion A of thescale member 1 at the same pitch as that on the portion A bysequentially sliding the mount 6 on the track 6, and in this case, thedistance B between the readout head 2 and the writing head 4 is selectedto be mh where the distance or pitch of the reference division linespreviously recorded is )t and m is an integer. This allows precisegraduation to be effected on a long scale member and hence enablesgraduation even after the scale member has been mounted on, for example,a large-sized machine tool, thus eliminating the difficultiesexperienced in the prior art.

Let it be assumed that the length of the scale member 1 is L, thedistance B between the readout head 2 and the writing head 4 is mh andthe length of the portion A is greater than the distance B. In thiscase, an error of the scale caused by the shift of the referencedivisions on the portion A results from, firstly, an error of thedistance B between the readout head 2 and the writing head 4 (B =m +e)\where e is the error, and secondly, an error of the divisions recordedon the portion A, if neglecting an error due to play of a machine toolemployed. These errors appear on a cycle of the distance 8 in any case,so that when no error exists in the divisions on the portion A as in thefirst case and B =ml\ +e A an error of 5A,, increases in a stepwisemanner at every cycle of 8, thus producing an error of Nelt in the end,as shown in FIG. 5.

This error can be corrected by rewriting the divisions after measuringthe error over the entire length of the scale member to find out e andadjusting the distance B correspondingly.

The error due to the second case repeats on a cycle of B but does notaccumulate, as depicted in FIG. 6, and in general this error is as smallas several microns and hence does not matter. Further, when the readouthead 2 is a multi-gap head, there is a tendency that small errors arecancelled by the averaging action of the head. Since this effect isrepeated at every cycle of B, errors decrease as the end of the scalemember is approached. With the recording device and method of thisinvention, substantially no error is introduced in graduation by meansof recording, and since graduation can be achieved after a plurality ofshort scale members have been joined together and there is nopossibility that errors are caused at the joints of the scale members.In addition, the divisions are sometimes recorded on the joints of thescale members, but the use of the aforementioned multi-gap head allowsreproduction of the recorded signals over a plurality of wavelengthsthereof and accordingly no problem is presented in this point. I

Therefore, according to this invention, metal, glass or like strips of asuitable length may be joined together as one assembly to form amagnetic gradient having precise graduations. Instead of such strip, along ribbonlike (tape-like) scale member may be used, which is fixed atboth ends to a support in a taut condition, and the support is attachedto a machine tool. In this case, it is preferred to attach a cushionmember, formed of a material such as commercially known under the nameof MOLTOPEN, to the back of the ribbon, and since the length of thedivisions becomes inaccurate when the ribbon is stretched, thegraduation by means of recording should be effected with the ribbonbeing subjected to the predetermined desired tension. It is alsopossible that the scale member is wound just like a tape measure withthe reference divisions being recorded on the top end portion thereof.

FIG. 7 illustrates another example of this invention, in which case agraduated scale member is placed in parallel with a scale member 1 to begraduated. A track 6 is disposed in parallel between the scale members15 and 1', by means of which a readout head 2 and a writing head 4 areslid along the scale members. That is, the readout head 2 is disposed incontact with the graduated scale member 15 and the writing head 4 isplaced in engagement with the scale member 1', under which conditionsthe reference divisions recorded on the portion A of the scale member 15are transferred onto the scale member 1. For this purpose, a coupler 17is employed and coupling rods 16 and 16' are attached thereto, on whichthe writing head 4 and the readout head 2 are respectively mounted.After the reference divisions have thus been recorded on the scalemember 1, precise graduation is carried out on the scale member 1 by theuse of the device and method depicted in FIG. I. This allows exactgraduation of a scale member held in taut condition and hence eliminatesthe possibility of introducing inaccuracy due to stretching of the scalemember as in the case of the reference divisions being previouslyprovided on the predetermined portion of the scale member. Substantiallyno error is caused by expansion of the scale member by selecting itsexpansion coefficient to be the same as that of the machine toolemployed.

The foregoing has described only several examples of this invention andthat various modifications may be effected in the construction of thedevice, the scale member and so on, if necessary, without departing fromthe novel concept ofthis invention. Further, this invention isapplicable not only to the making of a long and precise scale but alsoto the making ofa standard scale by precisely recording thereon oneportion of the divisions of an original standard scale. In addition,this invention enables graduation of a cylindrical drum and is suitablefor use in the case where signals of certain intervals are exactlyrecorded on a magnetic tape or the like. In the latter case, alternatingcurrent of constant frequency is usually recorded on the tape which isdriven at a constant speed, but precision with an error of less than 10cannot be expected because of wow and flutter. In the case of themagnetic scale, however, precision with an error of less than 10p. per 1m. can easily be obtained, so that if stretch of the tape is negligible,uniform recording with an error of I0 is possible. This is a veryeffective means for measuring wow and flutter of tape recorders.

I claim:

1. An apparatus for the magnetic recording of gradient information ontomagnetic media, comprising:

a length of recorded gradient information equal to ma where m is aninteger and k is the distance between lines of said gradient;

a support;

a first multi-gap head secured to said support; said head having gapstherein spaced by a distance which is a multiple of A,,,2;

a second head secured to said support and spaced from said firstmagnetic head a distance equal to nk where n is less than m, said firstand second magnetic heads positioned magnetically adjacent said lengthof recorded gradient information;

a member of magnetic material extending from said length of recordedgradient information and formed integrally therewith;

means for moving said support relative to said member; meanselectrically connected between said first and second magnetic heads,whereby movement of said first magnetic head along the length of saidrecorded gradient will record a second length of gradient informationonto said member immediately adjacent said length of recorded gradientinformation.

2. An apparatus for the magnetic recording of gradient information ontomagnetic media according to claim 1 further including means connectedbetween said second head and said support to adjustably position saidsecond head so as to obtain the distance nk 3. An apparatus for themagnetic recording of gradient information onto magnetic media accordingto claim 1 wherein said means electrically connected between said firstand second magnetic heads includes a detector having an input connectedto said first magnetic head and an output, a waveform shaping circuithaving the input thereof connected to the output of said detector andfurther having an output, and an amplifier having the input thereofconnected to the output of said waveform shaping circuit and the outputof said amplifier connected to said second magnetic head.

4. An apparatus for the magnetic recording of gradient information ontomagnetic media according to claim 1 wherein said predetermined distancebetween said first and second magnetic heads is less than the length ofthe recorded gradient information on said member.

5. A method for the magnetic recording of gradient information ontomagnetic media including'the steps of sequentially sensing magneticgradient information from a predetermined length of magnetic materialcontaining such information in increments spaced by a distance A, bymeans ofa multigap head having its gaps separated by a multiple of )t,2, and recording the length of recorded gradient information so sensedonto said magnetic material immediately adjacent said length of magneticgradient information.

1. An apparatus for the magnetic recording of gradient information ontomagnetic media, comprising: a length of recorded gradient informationequal to m lambda o, where m is an integer and lambda o is the distancebetween lines of said gradient; a support; a first multi-gap headsecured to said support; said head having gaps therein spaced by adistance which is a multiple of lambda o/2; a second head secured tosaid support and spaced from said first magnetic head a distance equalto n lambda o, where n is less than m, said first and second magneticheads positioned magnetically adjacent said length of recorded gradientinformation; a member of magnetic material extending from said length ofrecorded gradient information and formed integrally therewith; means formoving said support relative to said member; means electricallyconnected between said first and second magnetic heads, whereby movementof said first magnetic head along the length of said recorded gradientwill record a second length of gradient information onto said memberimmediately adjacent said length of recorded gradient information.
 2. Anapparatus for the magnetic recording of gradient information ontomagnetic media according to claim 1 further including means connectedbetween said second head and said support to adjustably position saidsecond head so as to obtain the distance n lambda o.
 3. An apparatus forthe magnetic recording of gradient information onto magnetic mediaaccording to claim 1 wherein said means electrically connected betweensaid first and second magnetic heads includes a detector having an inputconnected to said first magnetic head and an output, a waveform shapingcircuit having the input thereof connected to the output of saiddetector and further having an output, and an amplifier having the inputthereof connected to the output of said waveform shaping circuit and theoutput of said amplifier connected to said second magnetic head.
 4. Anapparatus for the magnetic recording of gradient information ontomagnetic media according to claim 1 wherein said predetermined distancebetween said first and second magnetic heads is less than the length ofthe recorded gradient information on said member.
 5. A method for themagnetic recording of gradient information onto magnetic media includingthe steps of sequentially sensing magnetic gradient information from apredetermined length of magnetic material containing such information inincrements spaced by a distance lambda o by means of a multi-gap headhaving its gaps separated by a multiple of lambda o/2, and recording thelength of recorded gradient information so sensed onto said magneticmaterial immediately adjacent said length of magnetic gradientinformation.